Prograde and near-peak zircon growth in a migmatitic pelitic schist of the southeastern Canadian Cordillera
Prograde and near-peak zircon growth in a migmatitic pelitic schist of the southeastern Canadian Cordillera
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加拿大科迪勒拉山脉东南部混合岩泥质片岩中锆石的顺行和近峰值生长
DOI：
10.1016/j.lithos.2017.02.016
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发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
J. Crowley
中科院分区：
文献类型：
--
作者：
F. Gervais;J. Crowley
在加拿大东南部科迪勒拉山脉混合岩泥质片岩的锆石上同时获取的 U-Pb 年代和微量元素与相平衡模拟的结果相关联。锆石生长的三个阶段中的第一个阶段发生在 77 到 72 Ma 之间，沿着蓝晶石 + 熔体场中湿法熔融和白云母脱水熔融反应 (675–775 °C) 之间的前行路径。这一持续增长阶段的特点是重稀土元素 (HREE) 呈浅正斜率。第二阶段发生在c。 69 Ma，在 775–875 °C 下黑云母脱水熔化后，石榴石显着生长，产生了贫重稀土的锆石。最后一个阶段发生在 c。 63 Ma 在逆行路径上，石榴石和金红石在 > 780 °C 时被消耗，如 HREE 和 Nb 的富集所示，但在熔体中长石结晶之前，如中等的 Eu 异常所示。该路径与本文和先前研究中分别记录的金红石和独居石岩石成因一致。与锆石生长的高温 (675–875 °C) 相比，钛锆石测温法得出的估计值低得不切实际 (470–739 °C)，低于湿固相线 80%；缓冲组合中不存在任何不确定性，因为金红石和石英始终存在，并且由于使用了压力相关校准，因此没有压力的影响。这项研究表明，锆石沿着顺行路径生长是可能的，并值得进一步研究控制变质岩中锆石测温的 Ti 含量的因素。
U–Pb dates and trace elements acquired simultaneously on zircon from a migmatitic pelitic schist from the southeastern Canadian Cordillera are linked with results of phase equilibria modeling. The first of three phases of zircon growth occurred between 77 and 72 Ma along a prograde path in the kyanite + melt field between the wet-melting and muscovite-dehydration melting reactions (675–775 °C). This protracted phase of prograde growth is characterized by a shallow positive slope in heavy rare earth elements (HREE). The second phase occurred at c. 69 Ma, after significant garnet growth by biotite dehydration-melting at 775–875 °C, which produced zircon depleted in HREE. The last phase occurred at c. 63 Ma on the retrograde path as garnet and rutile were consumed at > 780 °C, as indicated by enrichments in HREE and Nb, but prior to feldspar crystallization in the melt, as suggested by the moderate Eu anomaly. This path is consistent with rutile and monazite petrogenesis, documented herein and in a previous study, respectively. In contrast with the high temperatures at which zircon grew (675–875 °C), Ti-in-zircon thermometry yields unrealistically low estimates (470–739 °C) with 80% below the wet solidus; there are no uncertainties in the buffering assemblage, as rutile and quartz were present throughout, and no effect of pressure because a pressure-dependent calibration was used. This study demonstrates that zircon growth along a prograde path is possible and warrants further investigation on factors controlling the Ti content of zircon thermometry in metamorphic rocks.
加拿大南部科迪勒拉山脉偏碳酸岩和偏碱性岩石的 UâThâPb 地质年代学：地球动力学视角
影响因子：
3.5
作者：
Millonig;Gerdes
通讯作者：
Gerdes